Detailed Toxicity Information

Acute Toxicity 2

Ib, Highly
Hazardous
Not Listed
Not Available
No Consensus Value
No NTP Studies

Yes

2. The acute
toxicity reported on this page is of the pure chemical ingredient only and
may not reflect the acute toxicity of individual pesticide products. To view
acute toxicity of individual products, click on 'View Products' link in the 'Chemical
Identification' section above.

TRADE OR OTHER
NAMES

INTRODUCTION

Ethion
is an organophosphate pesticide used to kill aphids, mites, scales, thrips,
leafhoppers, maggots and foliar feeding larvae. It may be used on a wide
variety of food, fiber and ornamental crops, including greenhouse crops, lawns
and turf. Ethion is often used on citrus and apples (1,
5).
It is mixed with oil and sprayed on dormant trees to kill eggs and scales.
Ethion may also be used on cattle. It is available in dust, emulsifiable
concentrate, emulsifiable solution, granular and wettable powder formulations.
Products containing ethion must bear the signal word "Warning" (2).
EPA has established re-entry intervals of from 2 to 30 days, depending on the
crop, for ethion (8).

Ethion is one of a class of insecticides
referred to as organophosphates. These chemicals act by interfering with the
activities of cholinesterase, an enzyme that is essential for the proper
working of the nervous systems of both humans and insects. Please refer to the
Toxicology Information Brief on cholinesterase-inhibition for a more detailed
description of this topic.

TOXICOLOGICAL
EFFECTS

ACUTE TOXICITY

Ethion
is highly toxic by inhalation, dermal exposure, and ingestion. Like most
organophosphates, ethion is readily absorbed through the skin. Skin which has
come in contact with this material should be washed immediately with soap and
water and all contaminated clothing should be removed. It may cause contact
burns (11).
Ethion is almost non-volatile at normal temperatures, but when it is used as a
spray, it is easily inhaled (14).
If ethion is inhaled, runny nose and a sensation of tightness in the chest are
common complaints(12).
Persons with respiratory ailments, recent exposure to cholinesterase
inhibitors, impaired cholinesterase production, or with liver malfunction may
be at increased risk from exposure to ethion. High environmental temperatures
or exposure of ethion to visible or UV light may enhance its toxicity (6).

Ethion may be very irritating to the eye. It
caused slight inflammation and redness in the eye and skin, both of which
cleared within 48 hours. Ethion is not a skin sensitizer (8).

The organophosphate insecticides are
cholinesterase inhibitors. They are highly toxic by all routes of exposure.
When inhaled, the first effects are usually respiratory and may include bloody
or runny nose, coughing, chest discomfort, difficult or short breath, and
wheezing due to constriction or excess fluid in the bronchial tubes. Skin
contact with organophosphates may cause localized sweating and involuntary
muscle contractions. Eye contact will cause pain, bleeding, tears, pupil
constriction, and blurred vision. Following exposure by any route, other
systemic effects may begin within a few minutes or be delayed for up to 12
hours. These may include pallor, nausea, vomiting, diarrhea, abdominal cramps,
headache, dizziness, eye pain, blurred vision, constriction or dilation of the
eye pupils, tears, salivation, sweating, and confusion. Severe poisoning will
affect the central nervous system, producing incoordination, slurred speech,
loss of reflexes, weakness, fatigue, involuntary muscle contractions,
twitching, tremors of the tongue or eyelids, and eventually paralysis of the
body extremities and the respiratory muscles. In severe cases there may also be
involuntary defecation or urination, psychosis, irregular heart beats,
unconsciousness, convulsions and coma. Death may be caused by respiratory
failure or cardiac arrest (6).

Some organophosphates may cause delayed
symptoms beginning 1 to 4 weeks after an acute exposure which may or may not
have produced immediate symptoms. In such cases, numbness, tingling, weakness
and cramping may appear in the lower limbs and progress to incoordination and
paralysis. Improvement may occur over months or years, but some residual
impairment will remain (6).

The amount of a chemical that is lethal to
one-half (50%) of experimental animals fed the material is referred to as its
acute oral lethal dose fifty, or LD50. The oral LD50 for pure ethion in rats is
208 mg/kg. The oral LD50 for technical ethion in rats is 13 to 191 mg/kg, and
40 mg/kg in mice and guinea pigs (2,
6).
The dermal LD50 in rats is 62 mg/kg, 915 mg/kg in guinea pigs, and 890 mg/kg in
rabbits (6).

The lethal concentration fifty, or LC50, is
that concentration of a chemical in air or water that kills half of the
experimental animals exposed to it for a set time period. The 4-hour LC50 for
ethion in rats is 0.864 mg/l (2).

CHRONIC
TOXICITY

In a
chronic toxicity study with rats fed 0, 0.1, 0.2 or 2 mg/kg/day for 18 months,
decreased cholinesterase levels occurred in the high dose group. No other toxic
effects were observed. The NOEL for this study was 0.2 mg/kg (9).

Repeated or prolonged exposure to
organophosphates may result in the same effects as acute exposure including the
delayed symptoms. Other effects reported in workers repeatedly exposed include
impaired memory and concentration, disorientation, severe depressions,
irritability, confusion, headache, speech difficulties, delayed reaction times,
nightmares, sleepwalking and drowsiness or insomnia. An influenza-like
condition with headache, nausea, weakness, loss of appetite, and malaise has
also been reported (6).

Reproductive
Effects

A
3-generation reproduction study with rats given dietary doses as high as 1.25
mg/kg/day did not show any ethion related reproductive effects (8,
9).
Once in the bloodstream, ethion may cross the placenta (6).

Teratogenic Effects

When
rats were given doses of 0, 0.2, 0.6 or 2.5 mg/kg on days 6 to 15 of pregnancy,
developmental effects were seen only in the highest dose tested. In fetuses of
the high dose group, there was an increased incidence of delayed ossification
of the pubic bones. The developmental NOEL in this study was 0.6 mg/kg. When
rabbits were given doses of 0, 0.6, 2.4 or 9.6 mg/kg on days 6 to 18 of
pregnancy, fetuses from the highest dose tested exhibited an increased
incidence of fused sternal bones. The developmental NOEL in this study was 2.4
mg/kg (9).

Mutagenic Effects

Carcinogenic Effects

Ethion
was not found to be carcinogenic in rats and mice (8).
There was no increase in the incidence of tumors in rats fed dietary doses as
high as 2 mg/kg/day for 18 months. No evidence of carcinogenicity was observed
in mice fed dietary doses of up to 1.2 mg/kg/day for 2 years (9).

Organ Toxicity

Ethion
primarily affects the nervous system through cholinesterase inhibition, by
which there is a deactivation of cholinesterase, an enzyme required for proper
nerve functioning.

Fate in Humans and Animals

The
literature reviewed is not specific, but ethion is probably degraded in the
same general way as other organophosphates.

ECOLOGICAL
EFFECTS

Effects on Birds

Ethion
is highly toxic to practically non-toxic to birds, depending on the species.
Ethion is highly toxic to songbirds (LD50 in Red-winged blackbirds is 45
mg/kg). It is moderately toxic to medium sized birds such as bobwhite quail
(LD50 is 128.8 mg/kg) and starlings (>304 mg/kg). Ethion is practically
non-toxic to larger upland game birds (ring-necked pheasant) and waterfowl
(mallard duck) (9).

Because ethion is persistent in the
environment and because it is stored in plant and animal tissues, EPA is
concerned that ethion may adversely affect bird reproduction. EPA has called
for studies on the effects of ethion on bird reproduction (9).

Effects on Aquatic Organisms

Ethion
is very highly toxic to freshwater and marine fish and to freshwater
invertebrates (7,
8).
The 96-hour LC50 for ethion in rainbow trout is 500 ug/l (2).
The acute LC50 in Atlantic silversides is 49 ppb, 49 ppb in bluegill sunfish,
and in 720 ppb cutthroat trout and flathead minnows. The LD50 for freshwater
invertebrates is 0.056 to 7.7 ppb, depending on the species, and 5.6 to 49 ppb
for marine and estuarine invertebrates. Ethion accumulates in the tissues of
fish (8, 9).

Effects on Other Nontarget Species

Ethion
is practically non-toxic to honeybees. Its LD50 is 20.55 ug/bee (8,
9).

ENVIRONMENTAL
FATE

Breakdown of Chemical in Soil and Groundwater

Ethion
adsorbs strongly to soil particles and it is nearly insoluble in water. It is
therefore unlikely to leach or contaminate groundwater (3).
In soil, ethion is subject to microbial degradation. It is resistant to
hydrolysis, except in alkaline conditions (pH 9 or above) (4,
8).
Ethion is broken down in acids and bases. It is very slowly broken down in the
air (7).

Under laboratory conditions, the soil
half-life of ethion was 1.3 to 8 weeks, but in a greenhouse with an organic
soil, it was more persistent, with half-lives of 16 to 49 weeks, depending on
the degree of watering. When used repeatedly, ethion residues in soil will
increase from one year to the next (4).

Breakdown of Chemical in Water

Ethion
is almost insoluble in water (7).
In open waters, it is likely to adsorb to suspended particles and bottom
sediments. The persistence half-life of ethion varied from 4 to 22 weeks when
tested in three different natural waters under laboratory conditions. It breaks
down slowly in irrigation canal water (half-life = 26 days) (J. Agric. Food
Chem. 31 (4):704.1983). Its hydrolysis half-lives at 25 degrees C are 63, 58,
25 and 8.4 weeks at pHs 5, 6, 7 and 8, respectively. The half-life was 1 day at
pH 10 and 30 degrees C. Microbial degradation of ethion may be insignificant in
open waters. Volatilization be important only in shallow, rapidly moving
streams. Photo-oxidation may occur in sunlight. Bioconcentration of ethion may
be significant (4).

Breakdown of Chemical in Vegetation

No
information found.

Physical
Properties and Guidelines

Pure ethion is a colorless to light brown or
pale yellow liquid with no odor (2,
6).
Technical ethion has a very disagreeable odor. Ethion is stable under normal
temperatures and pressures if kept in a closed container, but it may oxidize
slowly if exposed to air. Ethion will hydrolyze in the presence of bases, acids
or lime (6).
Thermal decomposition of ethion may release toxic gases such as diethylsulfide,
sulfur dioxide, carbon monoxide, carbon dioxide, and phosphorus pentoxide (2).

Major tranquilizers (phenothiazines and
thioxanthines) may enhance the toxicity of organophosphates (Martin. Hazards of
Medication. 1971).

Persons who work with organophosphate
materials for long periods of time should have frequent blood tests of their
cholinesterase levels. If the cholinesterase level falls below a critical
point, no further exposure should be allowed until it returns to normal (10).

Protective clothing must be worn when using
ethion. Before removing gloves, wash them with soap and water. Always wash
hands, face and arms with soap and water before smoking, eating or drinking.
After work, remove all work clothes and shoes. Shower with soap and water. Wear
only clean clothes when leaving the job. Wash contaminated clothing and
equipment with soap and water after each use. Keep contaminated work clothes
separate from regular laundry (8).

EPA has assessed the risks of chlorpyrifos and reached an
Interim Reregistration Eligibility Decision (IRED) for this organophosphate
(OP) pesticide. Provided that risk mitigation measures are adopted,
chlorpyrifos fits into its own "risk cup"-- its individual, aggregate
risks are within acceptable levels. Chlorpyrifos also is eligible for
reregistration, pending a full reassessment of the cumulative risk from all
OPs.

Used on a variety of food and feed crops, golf courses,
as a non-structural wood treatment, and as an adult mosquitocide, chlorpyrifos
residues in food and drinking water do not pose risk concerns. With mitigation
eliminating virtually all homeowner uses, chlorpyrifos fits into its own
"risk cup." With other mitigation measures, chlorpyrifos worker and ecological
risks also will be below levels of concern for reregistration.

EPA's next step under the Food Quality Protection Act
(FQPA) is to complete a cumulative risk assessment and risk management decision
encompassing all the OP pesticides, which share a common mechanism of toxicity.
The interim decision on chlorpyrifos cannot be considered final until this
cumulative assessment is complete. Further risk mitigation may be warranted at
that time.

EPA is reviewing the OP pesticides to determine whether
they meet current health and safety standards. Older OPs need decisions about
their eligibility for reregistration under FIFRA. OPs with residues in food,
drinking water, and other non-occupational exposures also must be reassessed to
make sure they meet the new FQPA safety standard.

The chlorpyrifos interim decision was made through the OP
pilot public participation process, which increases transparency and maximizes
stakeholder involvement in EPA's development of risk assessments and risk
management decisions. EPA worked extensively with affected parties to reach the
decisions presented in this interim decision document, which concludes the OP
pilot process for chlorpyrifos.

Uses

·Chlorpyrifos
is an organophosphate insecticide, acaricide and miticide used to control
foliage and soil-borne insect pests on a variety of food and feed crops.

·Approximately
10 million pounds are applied annually in agricultural settings. The largest
agricultural market for chlorpyrifos in terms of total pounds ai is corn (~5.5
million).

Health Effects

·Chlorpyrifos
can cause cholinesterase inhibition in humans; that is, it can overstimulate
the nervous system causing nausea, dizziness, confusion, and at very high
exposures (e.g., accidents or major spills), respiratory paralysis and death.

Risks

·Dietary
exposures from eating food crops treated with chlorpyrifos are below the level
of concern for the entire U.S. population, including infants and children.
Drinking water risk estimates based on screening models and monitoring data from
both ground and surface water for acute and chronic exposures are generally not
of concern.

·In June,
2000, the Agency entered into an agreement with the technical registrants to
eliminate virtually all homeowner uses, except ant and roach baits in child
resistent packaging.

·Residential
postapplication exposures may occur after termiticide use in residential
structures. To mitigate risks from this use, the technical registrants agreed
in June 2000 to limit termiticide treatments to 0.5% solution, and cancel all
postconstruction uses. Pre-construction use will remain until 2005, unless
acceptable exposure data are submitted that show that residential
postapplication risks from this use are not a concern.

·Occupational
exposure to chlorpyrifos is of concern to the Agency. Exposures of concern
include mixing/loading liquids for aerial/chemigation and groundboom
application, mixing wettable powder for groundboom application, aerial
application, and application by backpack sprayer, high-pressure handwand, and hand-held
sprayer or duster. Generally, these risks can be mitigated by a combination of
additional personal protective equipment and engineering controls, and by
reductions in application rates. Additionally, the Agricultural Handler Task
Force will be developing exposure data to better characterize the risk from
certain uses (e.g., applying granulars by air).

·Risk
quotients indicate that a single application of chlorpyrifos poses risks to
small mammals, birds, fish and aquatic invertebrate species for nearly all
registered outdoor uses. Multiple applications increase the risks to wildlife
and prolong exposures to toxic concentrations. To address these risks, a number
of measures including reduced application rates, increased retreatment
intervals, reduced seasonal maximum amounts applied per acre, and no-spray
setback zones around water bodies will be needed.

Risk Mitigation

In order to support a reregistration eligibility decision
for chlorpyrifos, the following risk mitigation measures are necessary:

·There are
still some occupational risk scenarios that are still below the target MOE of
100, even with all feasible PPE or engineering controls. The risk assessments
for these uses will be refined with additional data.

·To
mitigate ecological risks the technical registrants have agreed to label
amendments which include the use of buffer zones to protect water quality, fish
and wildlife, reductions in application rates, number of applications per
season, seasonal maximum amounts applied, and increases in the minimum intervals
for retreatment.

·The
mitigation measures prescribed in the IRED along with mitigation that is
already being implemented as a result of the June, 2000, Memorandum of
Agreement, will reduce risk to both terrestrial and aquatic species. For
example, many of the reported incidents of wildlife mortality associated with
chlorpyrifos use were related to residential lawn and termite uses and use on
golf courses. The residential uses have been eliminated, the termiticide use is
being phased out, and the application rate on golf courses has been reduced
from 4 to 1 lb/ai/A. Additionally, no-spray buffers around surface water
bodies, as well as rate reductions for agricultural uses will be implemented as
a result of this IRED and will further reduce the environmental burden of
chlorpyrifos.

The OP Pilot Public Participation Process

The organophosphates are a group of related pesticides that affect the
functioning of the nervous system. They are among EPA's highest priority for
review under the Food Quality Protection Act.

EPA is encouraging the public to participate in the
review of the OP pesticides. Through a six-phased pilot public participation
process, the Agency is releasing for review and comment its preliminary and
revised scientific risk assessments for individual OPs. (Please contact the OP
Docket, telephone 703-305-5805, or see EPA's web site, Pesticide
Reregistration Status.)

EPA is exchanging information with stakeholders and the
public about the OPs, their uses, and risks through Technical Briefings,
stakeholder meetings, and other fora. USDA is coordinating input from growers
and other OP pesticide users.

Based on current information from interested stakeholders
and the public, EPA is making interim risk management decisions for individual
OP pesticides, and will make final decisions through a cumulative OP
assessment.

Next Steps

·Numerous
opportunities for public comment were offered as this decision was being
developed. In addition, the chlorpyrifos IRED has been issued with a public
comment period (see Pesticide
Reregistration Status).

·When the
cumulative risk assessment for all organophosphate pesticides is completed, EPA
will issue its final tolerance reassessment decision for chlorpyrifos and may
request further risk mitigation measures. The Agency will revoke the tomato
tolerance and amend the grape and apple tolerances for chlorpyrifos. For all
OPs, raising and/or establishing tolerances will be considered once a
cumulative assessment is completed.

Depending on the
degree of exposure periodic medical examination is indicated. Specific
treatment is necessary in case of poisoning with this substance; the
appropriate means with instructions must be available. If the substance is formulated
with solvent(s) also consult the card(s) (ICSC) of the solvent(s). Carrier
solvents used in commercial formulations may change physical and
toxicological properties. Do NOT take working clothes home. Dursban Dowco 179
Eradex Lorsban Pyrinex Coroban Danusban Terial are trade names.